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SDR Radios

One of the things I’ve been getting into recently is using Software Defined Radios (SDR) with cheap USB digital TV tuners that are available all over ebay, etc. These have been taking the radio community by storm as the chipset in them from RealTek can tune into a really wide band of frequencies. Usually from down around 20MHz, all the way up to nearly 2GHz.

Typical Digital TV stick with the Realtek chipset in

Tracking the skies

One of the fun and cheap projects you can do is track all the aircraft that are flying around you. All commercial and some light aircraft are required to have an ADS-B transponder that sends out a radio signal on 1090MHz that contains their location, speed, etc. These signals can be received with one of these SDR dongles and decoded to display this information on your computer.

There is even a ready made piece of software called dump1090 (and many, many forks of it) that will also display this information on top of a google map.

Current view of the planes around me

Antenna

The first thing you will need is a decent antenna for receiving these signals. The easiest to make is a quarter wave ground plane. In the simplest terms, this means that the main part of the antenna is a quarter of the wave length of the signal. The equation for this is:

f = c / λ

where f is the frequency, c is the speed of light in m/s, and λ is the wavelength. So to get the wavelength of 1090MHz, you rearrange the equation to:

λ = c / f

Putting the correct numbers into this means that a quarter of a wavelength is just 68.8mm. This makes for a pretty small antenna.

The ground plane is just four more wires at 90 degrees to each other, and bent down at a 45 degree angle.

All these wires are then soldered into a standard SO239 panel socket.

A quarter wave ground plane antenna for 1090MHz

There are many sites that will give a much better walk through of how to make one and the details behind it.

Software

Next, we need to look at the software. At this stage, if all you want to do is have a quick look for some fun, all you need is the antenna, usb stick, and the dump1090 software from one of the many forks (If found the dump1090-mutability one to be best). Download or clone this repo, and follow the compile instructions to give it a try. You should then be able to view the results either on screen or via a web browser.

The other option if you are going to go for a more permanent solution is to maybe use the data to improve a commercial sight such as FlightRadar24. This is what I chose to do, so I signed up for an account with them and followed the instructions to build a dedicated Raspberry Pi receiver that will automatically upload any information I receive to their systems, hence improving their reliability. This also gets you a full business account on there worth $500/year!

Enclosure

Lastly, if you’re doing a permanent solution, you need somewhere to put it. To save space and cost, I just used a Raspberry Pi with an decent sealed enclosure box.

Setup without the enclosure

I used some epoxy to glue the antenna on the end of some 20mm conduit that I had, with the cable passing down through it. Then drilled two holes in the box. One that I put a rubber grommet in to pass the power feed through, and the other to put an external antenna connector through.

Lastly, I used epoxy again to fasten some 20mm brackets to the box lid for the antenna to attach to. This was better than screwing, as fewer holes for moisture/bugs to get in through. Then I just mounted the whole thing on the side of my garage and passed a cable for power to it.

The whole unit is attached to the side of the garage

Ideally it would be placed higher, or at least the antenna would be, but that started to make things complicated. As it is, I can still get signals from planes nearly 200 nautical miles away.

Summary

Now I can access the Pi whilst I’m on my network and view all the planes around me. I also have a full business level account with FlightRadar24. Is there much point? Nope, not really apart from helping crowd source data for a company. Why’d I do it? Because I can and its fun!